Heat treating apparatus



illg. 25, 1959 o, E; CULLEN 2,900,990

HEAT TREATING APPARATUS Fuga Aug. 24, 1955 47 INVENTOA I O. E. CUL/LEN United States Patent t C HEAT TREATING APPARATUS Orville E. Cullen, Toledo, Ohio, assignor to Surface Combustion Corporation, Toledo, Ohio, a corporation of Ohio Application August 24, 1955, Serial No. 530,371

3 Claims. (Cl. 134-57) This invention pertains to the quenching of heat treated work and more specifically to apparatus for protecting hot quenching oil from deterioration due to oxidation.

Marquenching, as this hot quenching operation is commonly called, has become increasingly popular in recent years. Such an operation involves quenching a heat treated part in a medium maintained from 250 to 800 F. and more specifically from 275 to 400 F. By quenching in a medium at such temperatures, the exact temperature depending on the nature or composition of the steel being quenched, a martensitic structure may be attained in the steel and less warping or stress tends to occur in the work.

'I'he aforementioned quenching medium as employed in this process has generally consisted of an inorganic salt such as a mixture comprising sodium and potassium nitrates. Such salts are inherently oxidizing and consequently cause discoloration of the work. Where a protective atmosphere is utilized in the furnace heating chamber to prevent such occurrence during heat treating, it may be readily seen that a quenching process that defeats the objective of the use of a protective atmosphere has little merit. The use of such salts presents other Well known problems also such as sludging and possible explosions due to excessive heating. In carburizing processes, carbon carried into these salt baths from the carburized work may produce self-sustaining burning therein.

These inherent disadvantages have evolved a search for a better quenching medium. Oil, which possesses none of the above disadvantages and maintains bright surface work, had been excluded as a quenching medium in this type of process due to its rapid deterioration at marquenching temperatures. The life of oil employed in this process has been a matter of a few hundred hours after which the increased viscosity that occurs renders it useless. Although oil is initially less expensive than salt baths, the short lifeof oil has prevented its utilization in all but very specialized operations in which no substitute is feasible.

Recently, it has been discovered that by preventing the hot oil from being exposed to the air, oxidation is prevented and useful oil life may be increased to several thousand hours. `This has enabled oil to become an economically feasible medium in marquenching operations. The method of excluding air has been to maintain a gas containing no free or elemental oxygen over the surface of the oil in an enclosed quench tank.

In a carburizing furnace, for example, the work is placed in a charge vestibule which is then purged with an elemental oxygen free gas to eliminate air that entered as the work was charged therein; an inner door between the charge vestibule and furnace chamber is then opened and the work, generally held by trays, is transferred thereinto. A discharge vestibule is likewise used to prevent contamination of the atmosphere inside the furnace chamber. An inner door between the furnace chamber and discharge vestibule is opened, the treated `furnace chamber and vestibules.

Patented Aug. 25, 1959 work is transferred to an elevator within the latter ves- After the work has been quenched to the approximate temperature of the quenching medium, the elevator is raised, an outer door `is opened, and the work is discharged. With the outer door again closed, the discharge vestibule is similarly purged to expel oxygen and the furnace is ready for another cycle. Such cycles may be repeated as frequently as every few minutes. This necessitates fast purging of the charge and discharge vestibuleS-the shorter or more frequent the cycle, the greater the volume of purge gas per unit of time to effect adequate purging. To achieve this, a larger generator of the gas must be employed which results in higher initial cost of equipment. As an alternate, the size or volume of the vestibules may be kept to a minimum to assure sufficient purging with a smaller volume of gas.

I'he preferred operating practice for purging is to purge 'with a volume of gas approximately equal to tive times the volume of the vestibule to assure oxygen and oil vapors are removed. Thus, it may be seen that any additional volurne in a vestibule will increase the amount of purge -gas by approximately five times that amount and accordingly require a larger generator. When an elemental oxygen free gas is used as a protective covering over hot quench oil, such additional gas must be supplied the discharge vestibule to provide this, the quench tank being located below this vestibule and actually forming an integral part thereof.

Furthermore, in a carburizer, and some other furnaces, an explosive gas is employed as an atmosphere in the If this gas is used directly over the quench oil hazardous conditions result since the temperature of the gas is below its ignition temperature of approximately l300 F. Thus, any air leakage that may occur, particularly around the top of the quench tank, will create a combustible mixture with the gas and any ignition `would then cause a serious explosion.

In View of the above factors, an inert gas, separately generated, is now commonly employed above the quench oil except in the quench chute area in which the oil is still covered by the vestibule gas, the two gases being separated by a chute skirt extending from the quench chute to below the surface of the oil. This somewhat decreases the amount of gas required to purge the discharge Vestibule and also reduces the explosion hazard. The latter is not eliminated, however, since some of the explosive i purge and vestibule gases. This method also requires an additional generator to produce the inert gas.

To eliminate these disadvantages I have invented an enclosed quench tank, open to the `discharge vestibule only through the quench chute and in which oil is safely maintained at a high level.

An object of my invention is to lengthen the life of oil used in marquenching operation while decreasing the number and size of the generators used to produce atmosphere i gases for the furnace and for the protective atmosphere over the quench oil. The number is reduced by employing but one gas for both purposes and the size is reduced by decreasing the volume of gas necessary over the quenching oil.

In addition, the explosion hazard normally present in this operation is reduced, and a chute skirt now necessary when two separate gases are used is eliminated.

For further consideration of what is novel and my invention, refer to the drawing and following specification.

ln the drawing:

Figure l depicts a partially cross-sectional view of a furnace embodying my invention,

Figure 2 more aptly shows a detail of Figure l, and

Figure 3 illustrates an electrical circuit which may be embodied in my invention.

A carburizing furnace 11 comprises a charge vestibule 12, a heat treat chamber 13, and a discharge vestibule 14. Atmosphere gas is supplied by a generator and piping (not shown) to each of the vestibules and the heat treating chamber. Purge gas for the vestibules also may be supplied by this generator or an additional one. A quench tank 15 is located directly below vestibule 14. Work is fed to charge vestibule 12 through door 16 on trays such as 17. These trays may ride on rollers 18 through the entire -furnace and are commonly motivated by a pusher mechanism or by rotation of the rollers by an external driving force, neither of which is shown.

Subsequent to the work and tray entering chamber 13, a purge gas purges all air from the vestibule 12 that may have entered while door 16 was open and the tray was charged. The inner door 2i) is then raised into enclosure 21 and the tray transferred to heat treating chamber 13 by one of the above mentioned motivating means. As one tray enters the charge end of chamber 13 another is transferred to the discharge vestibule 14. Thus, doors Ztl and 21 are simultaneously raised into the respective enclosures 21 and 23. lt may be noted that both enclosures are fplaced on the heat treating chamber side of the door seals 19 and 29 to eliminate the necessity of purging these additional spaces each time the vestibules are purged. Door 22 is closed and tray 17, now resting on elevator platform 24, is lowered for a predetermined length of time into quench tank 15. After raising of platform 24, door 25 is opened and the work discharged. Once again vestibule 14 is purged and the furnace is ready for another cycle of charging, heating, quenching, and dischargmg.

Elevator platform 24 may be raised and lowered by means of chains or rods 26 and guided by guide rails 27. A lower portion of the travel of platform 24 may be laterally enclosed by sheet metal or the like attached to guide rails 27, thereby forming a vertical passage, the top and bottom of which are indicated by dotted lines 28, through which oil, circulated by propellers 3h, may be better directed. Guide means 39 are employed to direct the oil from propellers Sil to the vertical passage. Propeller shafts 31, supported by bearing blocks 32, are extended through walls 33, and driven by motors` 34. Heating of the oil to the required marquenching temperature is accomplished by radiant tubes 35 fired by burners 36.

The top 37 of quench tank 15 is tightly attached to Walls 33- and to quench chute 33 extending downward from vestibule 14. The chute has a cross-sectional area that is only slightly greater than elevator 24. By keeping this area at a minimum, the surface of the exposed oil is also a minimum. lt is preferable that top 37' be sloped as shown-downward from chute 38 to walls 33. This prevents any air from being trapped between the oil and the top should the level of the oil drop and subsequently be raised. Such air would markedly shorten oil life and create a serious explosion hazard. Furthermore, the oil is protected to a greater degree by this sloping because a drop in the oil level slightly below the bottom of quench chute Sii-Would expose the entire top surface of the oil, equal in area to the horizontal, cross-sectional area of the quench tank, if top 57 were level. With a sloping top, an equal drop in oil level would expose a surface only-slightly larger in area than they horizontal cross-sectional area of quench chute 38.

-A positive meansI of oil level control is illustrated in Figure 2. With no similar means provided, the oil level in a quench tank is subject to wide variation as the cold oil expands while the furnace is `being brought up to heat and is further heated as the hot work is immersed in it. The level must, of necessity be maintained well below the vestibule to assure no Ipossibility of the oil level rising into it. An explosion hazard is thus created due to the large volume `of gas being at a temperature below the ignition point of it. The additional space above the oil level also requires additional purge gas, either from a larger generator or from a supplementary one. In cases where a separate generator is used to produce gas 'for protecting all the oil surface except that exposed directly to the quench chute, a quench chute skirt must be extended down below the surface of the oil to separate the protective gas which is generally inert and the furnace atmosphere gas contained in the quench chute which may be explosive.

By the use of a positive means of level control the oil level may be maintained in the quench chute at a minimum distance below the vestibule. This eliminates the need of an additional gas to protect that surface of oil exposed in the quench tank outside t'he quench chute since no surface is `thus exposed, the surface being in direct contact with the top I37 of quench chute 15. A minimum of purge gas is required yalso since very little volume is contained between the oil level and vestibule. The explosion hazard is accordingly virtually eliminated and the need for a quench chute skirt is also no longer necessary.

In the level control of Figure 2, a float 40 is maintained in offset 41 by lever arm 42 pivoted at 43 and connected to a contact 44. Current is supplied to this contact 44 which is insulated from lever arm 42 and contacts 45 and 46 are wired to a relay valve 47 and a motor (not shown) for driving pump 48. In operation, if'the oil level becomes too lhigh contact 44 will make a circuit through contact 45 and open the normally closed valve 47. This allows oil to run through by-pass line 50 from tank 15 to reservoir 51. Similarly, with the level too low, a circuit will be effected through contact 46 thus operating pump 48 and driving oil from reservoir 51 back to tank 15. lf pump 48 is of such physical nature that the oil may readily flow back therethrough, the Valve 47 may be incorponated in the pump outlet pipe and the wiring be accordingly changed so that the valve is open lwhen contact 44 contacts either contact 45 vor 46. Thus, theV valve wil-l open when the oil level is too high to allow flow from tank 15 to reservoir 51 or when the pump is operating to permit flow from reservoir 51 to tank 15 by means of the pump.

Reservoir 51, provided with vent 57, need be Very small in comparison to quench tank 15 since it must contain only a volume of `oil necessary to maint-ain the level in quench chute 38, itself having a relatively small area. The oil in this reservoir is little above lambient temperature since the reservoir is small :and located `separately from the quench tank. Furthermore, the pipes connecting the two have large heat radiating surfaces in comparison to the volume of oil passing therethrough. The oil in this reservoir then need not -be isolated from the air due to its low temperature.

If the change in oil level is large enough to operate the above circuits every time work is ftransferred into and out of the oil, the upper and lower limits offoperation may be adjustedy by means of contacts 45 and 46 and lever arm 42 or by utilizing two separate float assemblies vertically spaced, one for each of contacts 45 :and 46.

The Icontrol wiring of Figure 2 is more clearly illustrated in the simple circuit of Figure 3. Here valve 47 and. pump motor 52 are operated by switches 53 and 54 respectively which represent contactsV 44 rand 45 and contacts 44 and 46 respectively. Current is supplied by lines 55 and 56.

Various modifications ot the level control Will be apparent to the reader. It is understood such modiiicat-ions may be employed without departing from the scope of my invention. A carburizing furnace has been used in the specication as an illustrative and not a limiting example. Many additional modications may be elected without departing from the scope of my invention or teachings contained herein.

I claim:

1. For a furnace having a discharge vestibule containing an element oxygen free gas atmosphere, a quench tank adapted to be located below said discharge vestibule for holding hot oil and comprising: a vertical quench chute adapted to extend down from said vestibule, a top connecting the bottom of said chute liquid-tightly to the tops of the walls of said tank and sloping downward thereto, and means for maintaining the level of the oil in the upper portion of said chute, means comprising: a oat in the upper portion of said chute; a first contact outside said chute; a lever arm connecting said float and said first contact, said lever arm being attached to a wall of said quench chute between said oat and said rst contact whereby said arm may vertically pivot; a second contact located above said tirst contact whereby said trst contact touches said second contact when the level of said oil falls to a predetermined point; a third contact located below said rst contact whereby said rst contact touches said third contact when the oil rises t0 a predetermined point; a reservoir located outside said tank and below the level of the oil in said tank; pump means for creating an oil flow from reservoir to said tank; rst pipe means connecting said reservoir and said tank through said pump means; a relay valve; second pipe means for connecting said tank and said reservoir through said valve, with said valve being normally closed; means for operating said pump means when said rst contact touches said second contact; and means for operating said valve when said rst contact touches said third contact.

2. For a furnace having a discharge vestibule containing an elemental oxygen free gas atmosphere, a quench tank adapted to be located below said discharge vestibule for holding hot oil and comprising: a verticle quench chute adapted to extend down from said vestibule, a top connecting the bottom of said chute liquid-tightly to the tops of the walls of said tank and sloping downward thereto, and means for maintaining the level of the oil in the upper portion of said chute, said means comprising:

a relatively small reservoir located outside said tank and below the level of said oil; pump means for creating a flow of oil from said reservoir to said tank; rst pipe means for connecting said reservoir and said tank through said pump; second pipe -means for connecting said reservoir and said tank; a relay valve located in said second pipe means; means for detecting the oil level in. the upper portion of said chute; means, responsive to said level detecting means, for operating said pump when the oil level in the upper portion of said chute falls below a. predetermined point; and means for opening said valve when the oil level in the upper portion of said chute rises above a predetermined point.

3. For a furnace having a discharge vestibule containing an elemental oxygen free gas atmosphere, a quench tank adapted to be located below said discharge vestibule for holding hot oil and comprising: a vertical quench chute adapted to extend down from said vestibule, a top connecting the bottom of said chute liquid-tightly to the tops of the walls of said tank and means for maintaining the oil level in said chute, said means comprising: a reservoir located outside said tank; means for detecting the oil level in said chute; means, responsive to said level detecting means, for transferring oil from said reservoir to said tank when the oil level in said chute falls below a predetermined point; and means, responsive to said level detecting means, for transferring oil from said tank to said reservoir when the oil level in said chute rises above a predetermined point.

References Cited in the tile of this patent UNITED STATES PATENTS 1,059,845 Delahunty Apr. 22, 1913 1,194,542 Raymond Aug. 15, 1916 1,671,635 Garcia May 29, 1928 1,959,215 Owen May 15, 1934 2,235,658 Waterman Mar. 18, 1941 2,374,535 Gibson Apr. 24, 1945 2,471,778 Ringer May 31, 1949 2,487,933 Martin Nov.`15, 1949 2,596,493 Linney May 13, 1953 2,638,909 Hiatt et al. May 19, 1953 2,639,047 Ipsen May 19, 1953 FOREIGN PATENTS 878,561 Germany Apr. 16, 1953 UNITED STATES PATENT OFFICE CERTIFICATE er CORRECTION Pete t No, 2,900,990 August 35, l Orville Geiler,

\ it is hereby certified that error ephpeers in the above numbered requiring correction and that the seid Lettere Patent lshould reed es @erDg recited below.,

In the heading to the drawing, line 2, and in the heading te the printed specification, line 2, title eff ifflvention, for "HEAT APPARATUS, each occurrence, reed. LIQ QUENCHNG APPARATUS uw;

column 5, line ll, for "an element" reed. elemental am; 18, before "mee11s insert seid line "from reeerveir n from seid reservoir f".

Signed and sealed this 23rd dey et T9613.,

(SEAL) Attest:

t H m i KARL ALIM' ROBERT c., wATsoN Attesting Officer I CorrmisssionerI ofv Patents 

